A. Field of the Invention
This invention relates to a method and an apparatus for modifying a production plan and, more particularly, to a method and apparatus for interactive modification of a production plan to achieve load balancing using a graphical user interface.
B. Prior Art
Conventional production plan modification techniques such as flat distribution or load-balancing are often expressed in the form of a spread sheet. When expressing a production plan in the form of a spread sheet, in general, different kinds of products are placed on the ordinate of a table while the time base is placed on the abscissa, so that the respective production quantities (numerical value data) of products to be produced in a unit period (month, week, day or hour) are sequentially entered in different cells. In order to modify the production plan, a user either manually rewrites such respective cell values when desired, or the cell is automatically rewritten by a recalculation mechanism of the spread sheet program. The production plan modification method using a spread sheet program involves the problems set out below.
1). Complicated manual calculation by the user is required.
When the user modifies a part of the production plan while maintaining a constant production quantity of a predetermined product, he must calculate manually the production amount required in addition to the automatic calculation by the recalculation mechanism of the spread sheet program.
2). The entire pattern is not readily comprehensive.
It is difficult to confirm the overall changes and the entire pattern of the production plan, with only the enumeration of numeral values provided by the spread sheet program.
There is also a more primitive method in which a load-accumulation graph is depicted on paper, without using a spread sheet program. The load-accumulation graph is used when displaying the total production load of a plurality of products as a single representation. There is no conventional method of modifying a production plan on a load-accumulation graph. It is always necessary to rewrite at least a part of the graph.
The following references are related to the present invention.
JPUPA (Japanese Published Unexamined Patent Application) No. 61-229164 discloses direct manipulation using a screen display to modify original data on a business chart. The publication, however, does not suggest any specific model to display the production plan.
JPUPA No. 2-73458 discloses a method for executing the recalculation of a spread sheet in a required direction. The publication, however, does not teach how to express the production plan.
JPUPA No. 58-64563 discloses interactive production planning, using a representation on a display device. In the publication, however, what is represented are the limiting conditions for the production plan; the production plan itself is not represented. This publication does not teach manipulation through the screen display for direct modification of a graphical representation of the production plan. Further, the publication does not teach the concept of primitive tasks to provide a constant work amount as will be described below.
JPUPA No. 62-224561 discloses the use of color distinction to distinguish the degrees of production load (work amount) of a production plan. In the publication, a production plan is shown by a matrix, with the work in rows and the time in columns, so that degrees of production load are color-displayed at respective positions of the matrix. The publication teaches neither the concept of direct modification of a graphical display of a production plan through interactive manipulation of the figure on the screen display, nor the concept of primitive tasks for providing a constant work amount.